Help with Midterm Review for Test

Please help with this calculus Mid-term review question. I have 12 more of these questions to go and I don't have a clue how to do this. I'm a beginner at calculus.

For the given cost function C(x) = 54sqrt(x)+ x^2/421875

a.) The cost at the production level 1450= My answer: $2061.242443
b.) The average cost at the production level 1450= ?
c.) The marginal cost at the production level 1450=?
d.) The production level that will minimize the average cost=?
e.) The minimal average cost=?